Single Frequency Networks (SFN)

Who has experience about SFN in Australia, please tell me the distance between transmitter in reality? In theory with mode 8K, guard interval: 1/8, 64QAM, the maximum distance's about 67km, but it uses for outdoor. Because attenuation of signal receive indoor, so the distance's smaller than in theory. Some one told me, in Berlin (Germany) they use 310m hight antenna but the distace between transmitter's only about 5km.

And please tell me how to solve black spot problem (Ex. Change power transmitter, use gap-filler)? For example:

DistancesMain to Kings Cross 7 km (Sydney Harbour bridge causes attenuation and reflected signals. Skyscrapers protect the southern coverage area from Kings Cross from the main signal)Main to Manly/Mosman 13 km terrain shields the area from the main signalMain to Bouddi 39 km some terrain shieldingBouddi to Manly/Mosman 34 km no terrain shieldingBouddi to Gosford 11 km some terain shielding

Dear experts,
Please help me!!!.
In my project, we use SFN network to deploy the DVB-T.
Next time we have to test this SFN network, please tell what methods, deivces we can use and what parameters need to be tested ?.
Please note that we use transmitters from R&S manufacture with 3 types: 600w, 1.3kw and 2.7kw.
Looking forward to receive your informations.

Who has experience about SFN in Australia, please tell me the distance between transmitter in reality? In theory with mode 8K, guard interval: 1/4, 64QAM, the maximum distance's about 67km, but it uses for outdoor. Because attenuation of signal receive indoor, so the distance's smaller than in theory. Some one told me, in Berlin (Germany) they use 310m hight antenna but the distace between transmitter's only about 5km.

And please tell me how to solve black spot problem (Ex. Change power transmitter, use gap-filler)? For example:

As you see, there are 2 signals at TV but they're so weak and interfere other. In reality, what do you solve that problem.

Many Thanks in Advance.Waiting for your kind comments and information.

Hix, Anyone has experience about SFN interference ?Look at the picture again and look at next picture, there are some signals which are out of guard interval (words bold). View herePlease be kind tell me how to deal with the above problem ? Thanks.

Andy & Lunar_manSet the period at the bottom of the Central Coast Forum to all dates and then you can see the reports of SFN interference. There are also some antenna installers contributing to that forum.

The ABHN37 transmitter, Newcastle is 250 kW Erp horizontally polarised, omnidirectional and Wyong on the same channel but is vertically polarised and has an radiated power of 1.25 kW. This combination gives some problems

The SBS 38 transmitter, Newcastle is 500 kW Erp horizontally polarised, directional antenna, away from Wyong on the same channel but is vertically polarised and has a radiated power of 1.25 kW. This combination gives less problems.

Mt Sugarloaf (Newcastle) to Forresters (Wyong) 58 km straight line.

I do not live anywhere near this area. Antenna istallers with digital field strength meter can measure the guard interval (Which is the Adaptive equaliser mode which is used to determine the delay and strength of reflected signals or SFN settings.

Hix, Anyone has experience about SFN interference ?Look at the picture again and look at next picture, there are some signals which are out of guard interval (words bold). View herePlease be kind tell me how to deal with the above problem ? Thanks.

The picture you posted is NOT a real world impulse response, it has been set up in a laboratory, likely with a rohde & schwarz SFU. So the question you are asking about dealing with SFN interference makes no sense. So you must have access to a test laboratory, so it is easy for you to figure out this problem for yourself. This board is for real world reception in consumer land, but I'm happy to answer any relevant meaningful questions (even though many contributors believe I don't know $h!t from clay).

Dear Alanh,
Could you tell me what is problem in SFN ?
We have 2 transmitter stations: Tx1 and Tx2. And we want to test signal some places between Tx1 and Tx2.
In these places, we follow test case below:
- Tx1 OFF, Tx2 On: result signal is good
- Tx1 ON, Tx2 OFF: result signal is good
- Tx1 ON, Tx2 ON: result signal is not good ( MER decrease, so our equipment can not decode). And how can we solve this problem ?

Dear Alanh,Could you tell me what is problem in SFN ?We have 2 transmitter stations: Tx1 and Tx2. And we want to test signal some places between Tx1 and Tx2.In these places, we follow test case below:- Tx1 OFF, Tx2 On: result signal is good- Tx1 ON, Tx2 OFF: result signal is good- Tx1 ON, Tx2 ON: result signal is not good ( MER decrease, so our equipment can not decode). And how can we solve this problem ?

thanks & regards

Sounds like you don't have an SFN but rather two interferring transmitters!

Are the modulators locked to GPS (10MHz & 1PPS) and running in SFN mode?Is the Transport Stream SFN capable (GPS locked with a valid MIP inserted)?

Lunar_andy,
I agree with Rusty,
Also;
Does one transmitter have its antenna horizontally polarised and the receiver using that transmitter using a high gain horizontally polarised Yagi-Uda antenna.
Is the other transmitter's antenna vertically polarised and when the reciever is receiving that transmitter using a phased array antenna mounted so that its dipoles are vertical.

Additionally is the signal delay feeding the transmitters adjusted to make the signal arrive at halfway between the transmitters simultaneously. The relative delay may be adjusted to make the "centre point" over a less densely populated area.

Not only does the modulator and the upconversion oscillators have to be the same frequency in both transmitters, the source program must be identical except for the delays mentioned above.

Does one transmitter have its antenna horizontally polarised and the receiver using that transmitter using a high gain horizontally polarised Yagi-Uda antenna.Is the other transmitter's antenna vertically polarised and when the reciever is receiving that transmitter using a phased array antenna mounted so that its dipoles are vertical.

This is not a requirement for SFN operation, both TX's can be horizontally or vertically polarized, the STB front end deals with this as if the secondary signal is an echo of the primary.

Additionally is the signal delay feeding the transmitters adjusted to make the signal arrive at halfway between the transmitters simultaneously. The relative delay may be adjusted to make the "centre point" over a less densely populated area.

True, but what are the chances -in this particular case- that the RX is exactly in the middle.

Not only does the modulator and the upconversion oscillators have to be the same frequency in both transmitters, the source program must be identical except for the delays mentioned above.

Yes the oscillators have to be phase-locked to a common source, usually GPS derived 10MHz, but more importantly the modulators have to dispatch bit-identical data streams on every carrier. This is achieved by synchronising the Mega-frames between modulators. The Transport Stream has to contain MIP's to identify the Mega frame boundaries in relation to the 1 Pulse Per Second (GPS derived-) time base. If the MIP's are missing the modulators cannot be synchronised and the SFN will fail. SFN modulators that loose the MIP or the reference signal will usually mute their output so the TX will shut down.

Rusty,
All ACMA allocations use alternate polarisations moving in a particular direction. For example Bouddi and Wyong are vertically polarised and Gosford which is in between is norizontally polarised along with the high powered Newcastle transmitters.

The reason for this is to make the area where similar strength but delayed signals as small as possible.

All ACMA allocations use alternate polarisations moving in a particular direction. For example Bouddi and Wyong are vertically polarised and Gosford which is in between is norizontally polarised along with the high powered Newcastle transmitters.

Alan,

Some, or even most, but definitely not all. For instance SBS 34 from Artarmon, Kings Cross and North Head are all Horizontal and I'm sure there are other examples. From a network planning point of view it may well make sense to use H/V alterations, from a pure technical point of view it is not a requirement for every SFN.

Rusty,All ACMA allocations use alternate polarisations moving in a particular direction. For example Bouddi and Wyong are vertically polarised and Gosford which is in between is norizontally polarised along with the high powered Newcastle transmitters.

The reason for this is to make the area where similar strength but delayed signals as small as possible.

AlanH

What rot - the polarisation is the same as the analog polarisation and that was determined by completely different planning processes. There is absolutely no ACMA planning process which deliberately alternates polarisation of digital services at existing analog sites.

BTW, the enquiry is from a fellow in Vietnam experimenting with SFN operation. If he wants any useful advice he should talk to equipment manufacturers, talk to broadcasters or service providers like Broadcast Australia or read the appropriate engineering manuals. Posting to forums like this and respecting Alan's waffle is hardly a professional or even academic approach!

What rot - the polarisation is the same as the analog polarisation and that was determined by completely different planning processes. There is absolutely no ACMA planning process which deliberately alternates polarisation of digital services at existing analog sites.

BTW, the enquiry is from a fellow in Vietnam experimenting with SFN operation. If he wants any useful advice he should talk to equipment manufacturers, talk to broadcasters or service providers like Broadcast Australia or read the appropriate engineering manuals. Posting to forums like this and respecting Alan's waffle is hardly a professional or even academic approach!

Thanks all of you!
I can sure about our SFN network is satisfied all condition of SFN, include GPS, same TS with MIP, same frequency, TX with SFN mode.
And we using Horizontal polarised for all TX stations. About manufactures, they only provide equipment and it is difficult to ask them about problems like this.
Additionaly, the distance between Tx1 & Tx2 station about 15 km. So, i don't think it is effected by delay.
Sory for inconvenience, i have not really understood our problem. In your country, this problem does not happen ?

Thanks all of you!I can sure about our SFN network is satisfied all condition of SFN, include GPS, same TS with MIP, same frequency, TX with SFN mode.And we using Horizontal polarised for all TX stations. About manufactures, they only provide equipment and it is difficult to ask them about problems like this.Additionaly, the distance between Tx1 & Tx2 station about 15 km. So, i don't think it is effected by delay.Sory for inconvenience, i have not really understood our problem. In your country, this problem does not happen ?

Thanks & regard

Hi Lunar_man,

What sort of link is used to get the Transport Stream to the two transmitters? I assume that the stream is either ASI or IP based but regardless of that, the most important thing is to make sure that no rate adaptation takes place that destoys the timing constraint of the stream. Are they dedicated point-to-point (dark fibre) links or are they carried as a 'service' by a Telco?

I would expect the modulators to alarm if there were any discontinuities in the incoming stream.

Finally, what type of receiver do you test with, a domestic STB or a professional IRD?

What sort of link is used to get the Transport Stream to the two transmitters? I assume that the stream is either ASI or IP based but regardless of that, the most important thing is to make sure that no rate adaptation takes place that destoys the timing constraint of the stream. Are they dedicated point-to-point (dark fibre) links or are they carried as a 'service' by a Telco?

I would expect the modulators to alarm if there were any discontinuities in the incoming stream.

Finally, what type of receiver do you test with, a domestic STB or a professional IRD?

CheersRusty

Hi Rusty,Our transmission line using fibre point-to-point with IP. Then, IP signal is converted to ASI by IRD before put into trasmitter.If input signal is not good ( no input, no MIP, datarate, SFN delay...), the modulators will alarm. And we using Promax product to test signal.thanks & regardsLunar

Hi Rusty,Our transmission line using fibre point-to-point with IP. Then, IP signal is converted to ASI by IRD before put into trasmitter.If input signal is not good ( no input, no MIP, datarate, SFN delay...), the modulators will alarm. And we using Promax product to test signal.thanks & regardsLunar

Well, if we can trust the IRD's to recover the stream without shuffling packets (what brand are they?) then we should trust that the input to both tx's is correct.

As for the GPS timing, do you use an external GPS clock or has the R&S modulator a built in one? If they are external, are they the same make / model?

I have seen a case where two different GPS devices were used with different duty-cycles, one was 50%, the other's 1pps impulse was more a needle shape, say 10%. Depending on whether the R&S modulator uses the rising or falling edge of the impulse the outcome may be quite different.

I don't know the R&S product too well and I don't know whether you can select whether to use the rising or falling edge of the 1pps impuls, but it may be worth checking.

Well, if we can trust the IRD's to recover the stream without shuffling packets (what brand are they?) then we should trust that the input to both tx's is correct.

As for the GPS timing, do you use an external GPS clock or has the R&S modulator a built in one? If they are external, are they the same make / model?

I have seen a case where two different GPS devices were used with different duty-cycles, one was 50%, the other's 1pps impulse was more a needle shape, say 10%. Depending on whether the R&S modulator uses the rising or falling edge of the impulse the outcome may be quite different.

I don't know the R&S product too well and I don't know whether you can select whether to use the rising or falling edge of the 1pps impuls, but it may be worth checking.

CheersRusty

Hi Rusty,thanks for your information.Sory for inconvenience, but maybe you are understanding wrong about our problem.Please note the, our SFN network run good almost places.ONLY!!! some places happen this problem as i said.thanks & regards